Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-01-15
2002-06-04
Vu, Huy D. (Department: 2664)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S337000, C455S446000
Reexamination Certificate
active
06400697
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
The subject matter of the present application is related to the subject matter of U.S. patent application Ser. No. 08/775,466 entitled “Method and Apparatus for Providing High Speed Services Using a Wireless Communications System” to Thomas K. Fong, Paul Shala Henry, Kin K. Leung, xiaoxin Qiu, Nemmara K. Shankaranarayanan and assigned to AT&T Corp., filed on Dec. 30, 1996, U.S. patent application Ser. No. 08/832,546 entitled “Method and Apparatus for Resource Assignment in a Wireless Communications System” to Xiaoxin Qiu and Kapil Chawla, filed Apr. 3, 1997 and U.S. patent application Ser. No. 08/982,510 entitled “Dynamic Resource Allocation Method and Apparatus for Broadband Services in a Wireless Communications System” to Kin K. Leung and Arty Srivastava, filed Dec. 2, 1997, the entire disclosures of which are hereby incorporated by reference.
FIELD OF THE INVENTION
The invention relates to wireless communications systems. More particularly, the invention relates to a method and apparatus for sector based resource allocation in a broadband wireless communications system.
BACKGROUND OF THE INVENTION
The need for high-speed broadband packet services will grow tremendously as telecommuting and Internet access become increasingly popular. Customers will expect high quality, reliable access to high-speed communications from homes and small businesses in order to access, for example: (a) the World Wide Web for information and entertainment; (b) office equipment and data from home at rates comparable to Local Area Networks (LANs); and (c) multimedia services such as voice, image and video. Although varying with application, effective broadband communication requires a bandwidth sufficient to permit a data rate up to the range of several tens of Mega-bits per second (Mbps).
Traditional wireless communications systems have a problem delivering high-speed services because of the amount of bandwidth these services require. Bandwidth is a key limiting factor in determining the amount of information that a system can transmit to a user at any one time. The concept of bandwidth may be better understood using an analogy. If information carried by a network were water, and links between communication sites were pipes, the amount of water (i.e., information) a network could transmit from one site to another site would be limited by the diameter of the pipes carrying the water. The larger the diameter of the pipe, the more water (i.e., information) can be transmitted from one site to another in a given time interval. Likewise, the more bandwidth a communications system has available to it, the more information it can carry.
Traditional wired communications systems using modems and a physical transmission medium, such as twisted pair copper wire, cannot currently achieve the data rates necessary to deliver high-speed service due to bandwidth limitations (i.e., small pipes). Promising technologies for “broadband” (i.e., large pipes) access include the Asymmetrical Digital Subscriber Loop (ADSL) and Hybrid Fiber-Coax (HFC). These wired-network approaches to providing high-speed access, however, could be expensive and time consuming to install.
The benefit of wireless systems for delivering high-speed services is that they can be deployed rapidly without installation of local wired distribution networks. However, traditional wireless systems such as narrowband cellular and Personal Communications Services (PCS) are bandwidth limited (small pipes) as well. As an alternative, wireless solutions such as Multichannel Multipoint Distribution Service (MMDS) and Local Multichannel Distribution Service (LMDS) have become attractive but these solutions presently offer limited uplink channel capacity. Moreover, these solutions in their current system design may not be capable of supporting a large number of users.
One solution for solving the bandwidth limitation problem for wireless systems is to maximize the available bandwidth through frequency reuse. Frequency reuse refers to reusing a common frequency band in different area, or “cells,” within the system. Refer, for example, to
FIG. 1
which shows a typical wireless communication system. A Base Station (BS)
20
communicates with several Terminal Stations (TS)
22
. The BS
20
is usually connected to a fixed network
24
, such as the Public Switched Telephone Network (PSTN) or the Internet. The BS
20
could also be connected to other base stations, or a Mobile Telephone Switching Office (MTSO) in the case of a mobile system. Each TS
22
can be either fixed or mobile.
The BS
20
communicates information to each TS
22
using radio signals transmitted over a range of carrier frequencies. Frequencies represent a finite natural resource, and are in extremely high demand. Moreover, frequencies are heavily regulated by the government. Consequently, each cellular system has access to a very limited number of frequencies. Accordingly, wireless systems attempt to reuse frequencies in as many cells within the system as a possible. To accomplish this, frequency reuse patterns are designed for cellular systems. A major factor in designing a frequency reuse pattern is the attempt to maximize system capacity while maintaining an acceptable Signal-to-Interference Ratio (SIR) for correct signal detection. SIR refers to the ratio of the level of the received desired signal to the level of the received undesired signal.
To achieve frequency reuse, a cellular system takes the total frequency spectrum allotted to the system and divides it into a set of smaller frequency bands. The geographic area covered by a cellular communications system is organized into cells and/or sectors, with each cell typically containing a plurality of communications sites, such as a BS
20
and TS
22
. The cells can be any number of shapes, such as a hexagon, and groups of cells can be formed with each cell in the group employing a different frequency band. These groups can be repeated until the entire service area is covered. Thus, in essence, the frequency reuse pattern determines the distance between cells that use common frequency bands. The goal of a pattern is to keep interference due to the common use of the same frequency band in different cells, or “co-channel” interference, below a given threshold to ensure successful signal reception. The advantage of this frequency reuse plan to manage co-channel interference can also be achieved by a time domain approach. In such an approach, the whole frequency spectrum is used for each transfer, but time is divided into frames, each of which consists of multiple frames. Different frames are reused in various cells in a way similar to frequency reuse patterns, as discussed above. Thus, there is a direct analogy between frequency bands and time frames.
Although the reuse of bandwidth in cellular systems is limited by this co-channel interference, directional antennas at both the BS and the TS in fixed wireless systems can help reduce the amount of interference from neighboring sectors and cells. U.S. patent application Ser. No. 08/775,466 discloses a Staggered Resource Allocation (SRA) method which uses a distributed, dynamic resource allocation algorithm for fixed wireless networks where the same spectrum is shared by every sector and cell on a dynamic, time basis. Relying on directional antennas to suppress interference, the algorithm schedules concurrent packet transmissions in various sectors and cells that cause little interference to each other, while sectors causing major interference to each other do not transmit simultaneously. There is a specific sequence in which sectors are labeled, and a specific schedule in which time sub-frames are used in each sector. As a result, the SRA scheme can yield a throughput in excess of 30% per sector for typical scenarios.
In such systems, a small fraction of terminals, typically near a cell boundary, will experience shadow fading conditions where interference cannot be adequately suppressed by the finite Front-to-Back (FTB) gain ratios of the terminal ante
Leung Kin K.
Shankaranarayanan Nemmara K.
Srivastava Arty
Nguyen Steven
Vu Huy D.
LandOfFree
Method and apparatus for sector based resource allocation in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for sector based resource allocation in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for sector based resource allocation in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2916938